The present invention generally relates to mobile telephone networks and, in particular, to timing control in uplink synchronous transmission in UTRA (Universal Mobile Telecommunication Terrestrial Radio Access) FDD (Frequency Division Duplex).
Basic third-generation mobile telecommunication, as used in Universal Terrestrial Radio Access Network (UTRAN), uses time alignment in an Uplink Synchronous Transmission Scheme (USTS) to preserve orthogonality between channelization codes from different UEs (User Equipment) and to properly de-spread the cell-specific long scrambling code. UTRAN is a conceptual term identifying a part of a radio communication network wherein a plurality of mobile terminals communicate with each other through one or more base stations. In particular, UTRAN identifies part of the network, which consists of radio network controllers (RNCs) and Node Bs between an interconnection point (Iu) and the radio interface (Uu). The interconnection point (Iu) is located between an NRC and a core network, and the radio interface (Uu) is located between UTRAN and the user equipment (UE). This is the starting point for the third generation mobile phone system UMTS (Universal Mobile Telecommunication System). The architecture of UMTS will include UTRA for radio access.
One of the modes of UTRAN for the user equipment (UE) is the FDD (Frequency-Division Duplex) mode, as distinguished from the time-division duplex (TDD) mode. UE radio transmission and reception (FDD) is described in the Technical Specification (TS) 25.101 v 3.1.0 (1999-12) of the Third Generation Partnership Project (3GPP) and documents referenced therein. In particular, the USTS is described in Study Report for USTS, 3GPP TSG RAN WG1#17 (Nov. 21-24, 2000), and the frame structure for downlink DPCH is described in TS 25.211 v 3.4.0 (2000-09).
In a USTS mode, the transmission time at the UE is controlled by two steps. The first step is Initial Synchronization and the second is Tracking.
As illustrated in FIG. 1, the downlink Dedicated Physical Control Channel (DPCCH) frame structure consists of radio frames. Each radio frame is 10 ms long and has 15 slots, and each slot carries control information in the forms of Pilot bits, Transport Formal Combination Indicator (TFCI) bits, and Transmit Power Control (TPC) bits. In the initial Synchronization step, transmission time is adjusted through the initial timing control information given by a higher layer, as described in 3GPP TSG RAN WG1#17 (Nov. 21-24, 2000). Before adjustment, a DPCH (Dedicated Physical Channel) message is expected to arrive at a Node B at point A, as shown in FIG. 2. In FIG. 2, xcfx84DPCH,n is a multiple of 256 chips offset and T0 is constant. After adjustment according to TINITxe2x80x94SYNC, the arrival of the PDCH message at Node B is scheduled to occur at point B, xcfx84DPCH,n+T0+Tref later from the beginning of each frame.
The reference time Tref is given to RNC as initial loading data, and the desired arrival time becomes xcfx84DPCH,n+T0+Tref. Since xcfx84DPCH,n=Tnxc3x97256 chip, Tnxcex5{0, 1, . . . , 149}, the desired arrival time may exist every 256 chips according to xcfx84DPCH,n. Different UE arrives at the cell at one of the desired arrival times according to xcfx84DPCH,n and the orthogonality among channelization codes can be preserved.
In the Initial Synchronization step, UTRAN obtains the round trip propagation delay (RTPD) by doubling the value of Physical Random Access Channel (PRACH) Propagation Delay measured accordingly to a method as specified in TS 25.215 V3.5.0 (2000-12) and sets the amount of adjustment for initial synchronization TINITxe2x80x94SYNC to compensate for the difference between the RTPD and Tref. UE adjusts its transmission time according to TINITxe2x80x94SYNC delivered from UTRAN. Since T0 is a constant (1024 chips) and Tref is a given value and the same for all UEs in a cell, after initial synchronization, the arrival can be controlled to occur at (xcfx84DPCH,n+T0+Trefxe2x88x921.5 chips, xcfx84DPCH,n+T0+Tref+1.5 chips) due to 3 chip resolution for reporting PRACH Propagation delay.
There may be variation around point B due to movement of UE, and the arrival of a DPCH message may be different from the desired arrival time. This difference can be eliminated by the Tracking Process using Time Alignment Bit (TAB) commands. In case of USTS, the TPC bits in slot #14 in frames with CFN mod 2=0 (even-numbered frames) are replaced by TABs. The procedure for the Tracking Process is as follows:
Node B compares the received arrival time with the desired arrival time from UE every 20 msecxe2x80x94the time period for two radio frames.
When the received arrival time is earlier than the desired arrival time at Node B, TAB is set to xe2x80x9c0xe2x80x9d. When it is later than the desired arrival time, TAB is set to xe2x80x9c1xe2x80x9d.
TAB replaces the TPC bit in slot #14 in frames with CFN mod 2=0.
At the UE, hard decision on the TAB shall be performed. When it is judged as xe2x80x9c0xe2x80x9d, the transmission time shall be delayed by xcex4T, whereas if it is judged as xe2x80x9c1xe2x80x9d, the transmission time shall be advanced by xcex4T. xcex4T is the timing control step size, whose minimum value depends on the oversampling rate.
Accordingly, the procedure keeps the uplink DPCCH/DPDCH (DPDCH=Dedicated Physical Data Channel) frame of a UE arriving at Node B at the same point of each frame.
As described before, a TAB is provided to the UE in each timing adjustment period, which is equal to two frame of 15 time slots. Thus, one out of 30 power control command (TPC) fields is punctured for USTS signaling purposes. In this prior-art signaling method, the searcher in the UE has only 20 ms to verify the position of the UE in time domain. For indoor/micro cells, this 20 ms time period is too short for most usable scenarios because the timing is changed with a much slower rate. If the TAB command is misinterpreted by the UE, the UE may adjust the timing opposite to what the Node B expects. In this situation, the searcher in Node B RAKE must verify the new position of the UE transmission in only 20 ms.
It is advantageous and desirable to provide a signaling method for timing adjustment in case of signaling errors so as to allow the searcher in the UE sufficient time to adjust the transmission timing.
The object of the present invention is to provide a robust signaling method for the uplink timing, whether to delay or to advance the transmission time, in an environment where signaling command transmission in the downlink may be subject to errors.
According to the first aspect of the present invention, a method for use in a frequency division multiplex (FDD) mode of a terminal of a mobile telephone network having a plurality of base stations capable of communication with the terminal over corresponding radio uplinks and downlinks, wherein the communication is carried out in radio frames and each radio frame for the radio downlinks comprises a plurality of time slots for carrying control information, and the control information includes a transmit power command, and wherein the terminal conveys a dedicated physical channel (DPCH) message to one of the base stations in each radio frame for the radio uplinks according to an uplink transmission time, and said one base station is capable of comparing a received time of the message to a desired arrival time for determining the time difference therebetween and assigning to the transmit power command a value indicative of the time difference, wherein the assigned value is equal to a first value if the received time is earlier than the desired arrival time, and the assigned value is equal to a second value if the received time is later than the desired arrival time. The method comprises the steps of providing the terminal M assigned values over a time period equal to N radio frame times, wherein N is an integer greater than 2; and adjusting by the terminal the uplink transmission time based on the assigned values over said time period.
Preferably, M is an integer ranging from 1 to N/2 and N is an even number, but M can also be an integer ranging from 1 to (N+1)/2 wherein N is an even number, or an integer ranging from 1 to N which is even or odd. Furthermore, it is preferred that the assigned values are assigned to the transmit power command in every other connection frame, but it is also possible to assign the assigned values to the transmit power command in every connection frame, so long as the time period is greater than 2 radio frame times.
Preferably, when M is greater than or equal to 2, the adjusting step is carried based on a sum of the assigned values.
Preferably, the assigned value is assigned to the transmit power command in the last time slot of the radio frame, but it is possible to assign the assigned value to the transmit power command in any one of the 15 time slots.
According to the second aspect of the present invention, an apparatus for use in a frequency division multiplex (FDD) mode of a terminal of a mobile telephone network having a plurality of base stations capable of communication with the terminal over corresponding radio uplinks and downlinks, wherein the communication is carried out in radio frames and each radio frame for the radio downlinks comprises a plurality of time slots for carrying control information, and the control information includes a transmit power command, and wherein the terminal conveys a dedicated physical channel (DPCH) message to one of the base stations in each radio frame for the radio uplinks according to an uplink transmission time, and said one base station is capable of comparing a received time of the message to a desired arrival time for determining the time difference therebetween and assigning to the transmit power command a value indicative of the time difference. The apparatus comprises a first mechanism, responsive to the time difference, for providing the terminal M assigned values over a time period equal to N radio frame times, wherein N is an integer greater than 2; and a second mechanism, responsive to the assigned values, for adjusting the uplink transmission time based on the assigned values over said time period.
Preferably, wherein M is greater than 2, the apparatus also includes a third mechanism for summing the M assigned values so as to allow the second mechanism to adjust the uplink transmission time based on the summed value.
According to the third aspect of the present invention, a mobile terminal for use in a frequency division multiplex (FDD) mode of a terminal of a mobile telephone network having a plurality of base stations capable of communication with the terminal over corresponding radio uplinks and downlinks, wherein the communication is carried out in radio frames and each radio frame for the radio downlinks comprises a plurality of slots for carrying control information, and the control information includes a transmit power command, and wherein the mobile terminal has means to convey a dedicated physical channel message according to an uplink transmission time to one of said plurality of base stations in each radio frame for the radio uplinks, and the received base station is capable of comparing a received time of the message to a desired arrival time for determining the time difference therebetween, and assigning to the transmit power command a value indicative of the time difference for providing to the terminal a signal indicative of the assigned value. The terminal comprises a first mechanism, responsive to the signal, for retrieving M assigned values over a time period equal to N radio frame times, wherein N is an integer greater than 2; and a second mechanism, responsive to the assigned values, for adjusting the uplink transmission time based on the assigned values over said time period.
Preferably, the terminal also includes a third mechanism for summing the assigned values when M is greater than or equal to 2, so as to allow the second mechanism to adjust the uplink transmission time based on the summed value.
The present invention will become apparent upon reading the detailed description taken in conjunction with FIGS. 3 and 4.